Electrical apparatus



1951 E. c. ILKER ELECTRICAL APPARATUS Filed Oct. 15, 1948 JNVENTOR. ELMER C. [LKE R QM v0 [ii/M ATTORNEY Patented Aug. 21, 1951 L CTRICAL APPARATUS Elmer C. Ilker, Wilmette, Ill., assignor to Essex Wire Corporation, Chicago, 111., a corporation of Michigan Application October 15, 1948, Serial N 0. 54,770

6 Claims.

This invention relates to anelectrical apparatus and particularly to a ballast for fiuorescent lamps. The invention in particular relates to a ballast which is corrected for power fac tor and is for use with one fluorescent lamp on an alternating current circuit whose potential is normally over one-half of the desired running potential.

The invention makes it possible to provide a simple and economical ballast which may be designed to operate in a satisfactory manner for both starting and running conditions. I The general background problem for this invention will most easily be understood after the specific invention has been described. I

The invention will be; described in connection with the drawing wherein Figure 1 is a circuit diagram illustrating the invention and Figure 2 is a plan view partly in section of a ballast embodying this invention.

Referring now to the drawing, a series of windings III, II, I2 and I3 are disposed upon leg I5 of laminated core 18. Leg l5 and opposing leg H are joined by short connecting legs I8 and I3 providin window 20. The relatively-close spacing between long legs I5 and I? of the core provides a substantial leakage path for magnetic flux. Other cores providing desired leakage may be used.

As shown in Figure 2, winding I is disposed over part of leg I and winding I I is disposed over winding I0. Disposed over the remainder of leg I5 is winding l2. Over Winding I 2 is winding I3. Windings I2 and I3 are closely coupled. Windings It] and Il are also closely coupled. Windings Iii and II are loosely coupled to wind ings I2 and I3, although the coupling to I3 is unimportant.

Windings I0 and Il may be one continuous winding with an intermediate tap." The same is true of windings I2 and I3. It is understood that the core is made up of conventional laminations to permit ready positioning of the windings. The junction of windings IE! and H is connected by lead 22' to condenser 23 whose other terminal is connected by lead 24 to the bottom end of winding 13. The junction of windings II and I2 is connected to wire 26 while the junction of windings I2 and I3 is connected to wire 21. Wires 26 and 27 are for connection to a conventional alternating current supply circuit.

The free end of Windin i0 is connected'by lead 30 to filament 3i and thence by lead 32 to starting switch 33. The circuit from starting switch 33 continues along lead 34 to filament 35. Filaments 3I and 35 are part of fluorescent lamp 3% of a type available on the market. The circuit from filament 35 continues by way of lead 31 to the junction of windings I2 and I3.

If winding Il is omitted, with Wires 22 and 26 connected together on the ballast, then the structure assumes a conventional form common in the prior art. It will be convenient to assume that winding II is omitted and discuss the shortcomings of the prior art.

When a lamp has broken down at the beginning of a cycle, the discharge has the nature of a glow or arc and has a negative resistance. For this reason, it is necessary that ballast means be provided to impart stability to the lamp circuit as a whole. After the discharge has been initiated, the lamp current should be limited to a predetermined figure to conform to the rated wattage of the lamp. As a rule, the limits for departure from such predetermined conditions are not very great, if maximum benefit from the lamp is to be assured.

When such a lamp is started, it is customary to dispose the filaments in series by means of a starting switch. The Wattage for and duration of preheating the lamp are interrelated and predetermined to conform to the specifications of both the lamp maker and starting switch maker. As a ru e, automatic starting switches are designed to maintain the filaments heated for a predetermined time. Hence the starting current for a lamp must in general conform to predetermined limits. Assuming the usual cycle volt supply, fluorescent lamps such as the 3G or 40 watt variety, require a specified 200 volts for running.

Referring now to the circuit diagram of Fig ure 1, minus winding II, the potential from line wires 26 and 2'! is stepped up by autotransformer action in windings IE and I2 to a potential suitable for lamp 36 under normal running conditions. Winding I 3 and condenser 23 operate in the usual manner for power factor correction. Under such conditions, the lamp presents a substantial resistance load and together with the reactance of the ballast limits the load current to a predetermined normal value.

Now assume that the lamp has started with switch 33 closed. The lamp load is practically zero and consists of the pure resistance of the two filaments in series. In comparison to the rest of the circuit, this is negligible. Hence at starting, the load may be considered as a short circuit. Still assuming that winding II is omitted, it will be apparent that the short circuit effectively disposes winding HI across winding I2. If windings l and I2 are designed to provide the normal potential for running conditions, saturation will occur in the magnetic circuit of winding [0 unless the step up ratio is 2 to 1 or more. It is readily seen that to produce this ratio when not required otherwise, will result in a transformer design of higher volt ampere capacity also requiring greater power factor correction. This condition could also be overcome by a specially designed core structure at the expense of an inefficient use of core material and space.

It ispossible to maintain winding It] at the value for running conditions and operate the core at a low flux density. Then at starting, the flux density will be increased to a normal value. This however represents a wasteful use of iron, making the ballast expensive and bulky.

The running conditions will not be adversely afiected if starting conditions are favored, but rather the design must be based on considerations of the worst or most extreme conditions. Generally, this would be the starting conditions. The result is that the design for running conditions would be too conservative or ineflicient so far as the cost of constructing the ballast is concerned.

This invention varies the circuit so that a circuit parameter is provided which is not equally eifective for both starting and running. Thus the number of turns of winding 1 I, within limits, may be varied and when so varied will have a substantial effect upon the starting current but have negligible eifect upon the running power consumption of the lamp. It has been found that when winding H has more turns that the starting current is decreased. As a rule, Winding [I may have from about up to about 20% of the turns of winding ID. Preferably the ratio is from about Z /2% to about 15%.

The arrangement of the windings, as regards coupling, is shown in Figure 2. The design of a ballast in general will follow along conventional lines. Thus the turns and turn ratio of windings HI and I2 will generally follow conventional lines. Similarly winding :3 and condenser 23 will follow conventional values. It is understood that the value of condenser 23 is one of the parameters in the design of a ballast, this being Well understood in the art.

The turns making up winding l I will be found to have a highly beneficial governing effect upon the intensity of the starting current. The Value of winding l l for most eflicient results will be dependent upon the precise values of the remainder of the windings, value of condenser and dimensions of the core.

In large measure, the exact design is a function of desired characteristics of the ballast. The ballast casing is usually of iron and sufficiently close to the windings and core so that it has substantial effect upon the performance of the ballast. Thus the casing will also have to be considered.

Preferably the circuit containing the condenser is designed so that the current therein under running conditions is about equal to the normal running current through the lamp. The current in the condenser circuit does not change greatly from starting to running.

Winding II has the currents therein generally more than 90 out of phase with currents in winding l0. Hence it is possible to use finer wire for '4 I generally simpler to wind f0 and H as one continuous coil and take a tap off for wire 22. In any event the internal losses contributed by the addition of winding II will be negligible.

The new ballast, when operating under starting conditions, will be found to limit the starting current to a desired value substantially below what would ordinarily be the case if winding II were omitted. At the same time the core may be designed for eflicient and effective operation under running conditions and starting conditions.

What is claimed is:

1. A ballast for fluorescent lamps of the type having two separate filamentary cathodes with a starter switch connected between one terminal of one cathode and one terminal of the other cathode, said lamp having both filamentary cathodes connected in series upon starting and drawing a heavy current to energize both cathodes, said ballast comprising a ferromagnetic laminated core having substantial leakage flux, four windings connected in series and disposed on said core, the first and second windings being magnetically additive and closely coupled, the third and fourth windings also being magnetically additive and closely coupled, the first two windings being loosely coupled to the last two windings, said first winding having one free terminal forming a ballast terminal for connection to the other terminal of one cathode, the terminals of the third winding forming ballast terminals for connection to an alternating current power line, the common terminal of the third and fourth windings forming a ballast terminal for connection to the other terminal of the other cathode, a condenser connected across the second, third and fourth windings, said second winding having less than 20% of the turns of the first winding, the first and third windings being proportioned to provide rated running current to the lamp with the running potential across the first winding being less than the normal potential across the third winding, said condenser and fourth winding being proportioned to provide power factor correction during running, said second winding having negligible effect under running conditions but effective under starting conditions to reduce current through the first winding whereby the core may operate under both starting and running conditions at normal flux densities, without substantial saturation at starting or without magnetically inefficient low flux density under running conditions.

2. The ballast, according to claim 1, wherein said second winding has between about 5% and 20% of the turns of the first winding.

3. The ballast, according to claim 1, wherein the second winding has between about l /2% and about 15% of the turns of the first winding.

4. The ballast, according to claim 1, wherein the ferromagnetic core has a generally rectangular outline with a long narrow window and wherein the four windings are divided into two groups in side by side relation on the long leg of the core, each group consisting of an inner winding and an outer winding, the two windings in a group being closely coupled.

5. The ballast, according to claim 1, wherein the ferromagnetic core has a long, narrow, generally rectangular window with the four windings disposed on a long leg, the first and second windings forming one group and the third and fourth windings forming another group, said two 6. The ballast, according to claim 1, wherein 6 the ferromagnetic core is shaped to provide a long, narrow, generally rectangular window with all windings disposed upon a long leg, said first and second windings forming one group and said third and fourth windings forming a. second group, said two groups of windings being disposed in side by side relation, each group having the windings arranged to provide inner and outer windings, the second winding having be- 6 tween about 7 and 15% of the turns of the first winding.

ELMER C. ILKER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 10 Number Name Date 2,025,471 Osborne Dec. 24, 1935 2,352,073 Boucher & Kuhl June 20, 1944 2,446,152 Alford July 27, 1948 2,458,277 Lark et al. Jan. 4, 1949 2,487,092 Bird Nov. 8, 1949 

